I’m trying to find out what purpose this type of design serves and how they are designed but have hit a wall with knowing what to even look for.
This piece of the voron stealthburner is the only example I can think of off the top of my head but I have seen them before in some sort of fan duct or funnel thing.
The hub mostly reduces turbulence in the flow as well. Depending on if it’s on then intake o exhaust , it also has a number of effects.
As an intake, it compresses the incoming flow, as it comes to the blades with less drag- which makes the fan much more effecient.
As an exhaust, does the same, but would also expand the cross section (which slows the airflow,) it looks like the duct also constricts, though, so rather than changing the speed of the airflow, it’s removing the center void created by then fan’s own hub.
Which again smooths out the flow and makes it more effecient for whatever it’s hitting